The results of a study of pediatric influenza mortality for 3 influenza seasons (2004-2007), by investigators at the Centers for Disease Control and Prevention (CDC), were published in the October 2008 issue of Pediatrics. The authors report an increase in the incidence of bacterial co-infection in fatal pediatric influenza from 6% to 34% over the 3 year period. The chief pathogen was Staphylococcus aureus, with 64% of S.aureus isolates displaying resistance to methicillin (i.e. MRSA). Among the S.aureus co-infected children, pneumonia and acute respiratory distress syndrome (ARDS) were more common complications than in those not harboring the organism. Additionally, progression to death was quite rapid, occurring within 72 hours of onset in 45% of fatalities. Only 6% of victims who met indications for vaccination were fully immunized.1

The study data was collected from reports of pediatric influenza deaths to CDC by state and local health departments, a requirement since October 2004. In total, 166 influenza-associated pediatric deaths were reported by 41 jurisdictions. The average age of the decedents was 5 years, and 45% of those studied had an Advisory Committee on Immunization Practices (ACIP) high-risk condition, such as asthma or cerebral palsy. While 45% of the victims died within 3 days, the median time between onset and death was 4 days, and 44% died at home or in the emergency department.1

S.aureus-associated Complications

Bacterial co-infection among fatal pediatric cases was found to increase over the 3 seasons, peaking in 2006-07 with a rate of 34%. S.aureus was the major pathogen in each season. Older age, a higher prevalence of a radiographically confirmed pneumonia (64% vs. 28%), and a higher incidence of ARDS (45% vs. 10%) were found to be significantly more common in those co-infected with S.aureus.1

Importance of MRSA

Although pediatric deaths from influenza remain rare, this study emphasizes the role of bacterial co-infection, exemplified by S.aureus, as an important etiologic factor that can result in deaths of pediatric flu patients. As indicated in a recent study, bacterial superinfection may have played a significant role in many deaths during the 1918 influenza pandemic.2 The emergence of MRSA, and possibly its toxin-laden USA 300 strain, as the major bacterial co-pathogen may be behind the increased severity of illness seen in these patients.3

Call for Vaccination

Also underscored is the importance of vaccination in attenuating and halting influenza infection. Of note, the most recent CDC guidelines call for vaccination of all children above 6 months of age4, and a recent study by Zaman and colleagues highlighted the role of maternal immunization during pregnancy in protecting infants too young to receive the vaccine themselves.5